This invention relates to a sliding bearing which exhibits excellent bearing properties even in a high-load range, that is, under severe conditions of use in a recent internal combustion engine designed to produce a high power.
A conventional copper alloy sliding bearing used in an internal combustion engine comprises three layers, that is, a steel back metal layer, a copper alloy layer and an overlay. The copper alloy layer, extensively used in high-speed, high-load engines, is composed of a Cu-Pb alloy or a Cu-Sn-Pb alloy, and the overlay is composed of a Pb-Sn alloy, a Pb-Sn-Cu alloy, or a Pb-Sn-In alloy.
In most cases, the steel back metal layer is composed of low-carbon steel whose carbon content is not more than 0.2%.
In recent internal combustion engines, the housing of the bearing is liable to be deformed by an inertia force because of the high-speed, high-load design of the engine. This deformation adversely affects the tight fit between the bearing and the housing, and damage, such as fatigue and seizure due to fretting (which means a surface damage developing when a slight relative motion is periodically repeated between two contact surfaces) or migration (which means a phenomenon that Cu-plating, flash-plating and carbide concentrate locally as a result of a periodic relative motion), develops. Therefore, it is necessary that the steel back metal layer of the bearing should be made of a hard, high-strength material, and that a larger interference should be provided when mounting the bearing on the housing so as to enhance the degree of tight fit of the bearing as well as the followability of the bearing (high "followability" of a bearing means that the bearing is able to be followable to the high level of deformation of a housing in which the bearing is fitted, so that the bearing can keep a satisfactorily fitting state on the housing even when the housing is deformed in a high degree) relative to the deformation of the housing. However, the conventional bearing having the steel back metal layer made of low-carbon steel has not been found entirely satisfactory in that it is low in strength, and will yield when the bearing is mounted on the housing with a large interference.